When bottles are treated in filling lines, and in particular when labels are attached to containers in labelers, it is often necessary to align the rotary positions of the containers so as to guarantee that there is a sufficiently large distance e.g. between a burr and the label and/or that the label is correctly positioned with respect to a glass embossment.
In this respect, it is known from EP 1 205 388 B2 to record, by means of four cameras, the outer surface of a container over the whole circumference thereof, to evaluate suitable features in the recorded images and to transmit to the drive system instructions for rotating the container about its longitudinal axis to a desired position.
In apparatuses of this kind the container is rotated at a constant angular speed which has to be observed as precisely as possible when the features are being recorded. In addition, the containers to be aligned must be moved past the cameras at a constant speed, so that the rotary position of the containers and their position in the machine, e.g. the angular position of a conveying carousel in the machine, can be allocated precisely.
In view of inaccuracies (backlash, synchronized speed variations or the like) in the interaction between the drive systems, which rotate the container and move it past the cameras, and the trigger times at which the pictures are taken, the accuracy of the above described method is often insufficient so that a subsequent fine adjustment of the containers with the aid of a separate camera becomes necessary. To this end, additional machine positions have to be provided in the machine.
It is an aspect of the present disclosure to provide an apparatus and a method for exactly aligning the rotary position of the containers with little expenditure of time and little space requirement.
This aspect is achieved by a proximity switch for triggering an imaging function of the camera unit. This makes the triggering of individual camera images independent of synchronized speed variations. Since this increases the accuracy of image evaluation, the rotary position of the container can be corrected in one step, i.e. also without any fine adjustment. In addition, acceleration and/or deceleration ramps of the rotation of the container can be included in the recording of the feature, and the space required in the machine for this purpose can be utilized.
The proximity switch preferably comprises a plurality of trigger signal generators provided on the holder at predetermined rotary angle intervals and a stationary receiving unit including at least one trigger signal receiver. It is thus possible to generate trigger signals which depend primarily on the angle positions of the trigger signal generators. This allows a particularly precise determination of the rotary position and of the alignment of the container.
According to an advantageous embodiment, at least every third trigger signal generator is positioned opposite the trigger signal receiver, when it is at a rotary position at which it is located at a minimum distance from the receiving unit. This allows reliable triggering.
Preferably, the apparatus additionally comprises a conveying means which moves the holder along a reception area of the trigger signal receiver. It is thus possible to align a continuous flow of containers.
A plurality of trigger signal receivers is, in an advantageous manner, arranged in the receiving unit such that the conveying means moves the holder along the reception areas of the trigger signal receivers in succession. It is thus possible to trigger a plurality of cameras independently of one another.
According to a preferred embodiment, the trigger signal receivers are distributed over at least two planes which extend substantially parallel to the conveying direction of the conveying means. This allows an overlapping mode of arrangement of the trigger signal receivers.
The receiving unit comprises, in an advantageous manner, a plurality of trigger signal receivers, and the distances between neighboring trigger signal receivers are adapted to the profile of an acceleration and/or deceleration ramp of the rotary movement of the holder. It is thus possible to include acceleration and/or deceleration ramps in the recording of the feature and to provide the apparatus with a particularly compact structural design.
According to a particularly advantageous embodiment, the proximity switch is sensitive to magnetic fields. Magnetic proximity switches are particularly insensitive to soiling.
According to a preferred embodiment, the apparatus further comprises a computing unit for localizing a feature on the imaged container and for computing an actual rotary position of the container, and a control unit for effecting a movement to a desired rotary position of the container. It is thus possible to bring the container to a rotary position suitable for labeling.
The technical problem is additionally solved by a method in the case of which a proximity switch triggers the imaging of the container. This makes the triggering of individual camera images independent of synchronized speed variations. Since this increases the accuracy of image evaluation, the rotary position of the container can be corrected in one step, i.e. without any fine adjustment. In addition, acceleration and/or deceleration ramps of the rotation of the container can be included in the recording of the feature, and the space required in the machine for this purpose can be utilized.
According to a preferred embodiment, trigger signal generators rotate together with the container and at least every third trigger signal generator produces a trigger signal when it approaches a stationary receiving unit. This allows a reliable triggering, which is independent of synchronized speed variations.
A particularly advantageous embodiment is so conceived that, at a rotary position of the trigger signal generators at which the respective trigger signal generators are located at a minimum distance from the receiving unit, the trigger signal reaches a predetermined trigger level so that a trigger control signal is outputted, which triggers the imaging of the container.
A preferred embodiment is so conceived that, while the developed view of the container is being formed, the container is moved along at least one reception area of the receiving unit. It is thus possible to align a continuous flow of containers.
According to an advantageous embodiment, the trigger signal is generated in different trigger signal receivers of the receiving unit. It is thus possible to trigger a plurality of cameras independently of one another.
According to a preferred embodiment, the method further comprises the following steps: localizing a feature on the imaged container and computing an actual rotary position of the container; and effecting a movement to a desired rotary position of the container. The container can thus be brought to a rotary position which is suitable for labeling.